An ejector/eductor (those two words are used interchangeably) arrangement using a double walled duct mounted to the aft engine frame and method of reducing jet engine noise are disclosed wherein the primary combustion gas stream of the jet engine is ejected into a mixing section or zone of the double walled duct, into which a secondary external cool gas stream from ambient air is injected at a velocity sufficient to create a mixed flow condition, resulting in rapid mixing of the primary and secondary gas streams both in the mixing zone. The ejector, can be provided with means for adjusting the exit area of the mixing section or zone to match the engine operating conditions so as to create proper conditions within the mixing zone for noise suppression. Noise suppression by the method and means disclosed occurs at all frequencies with probably a minimal loss of thrust, and possibly a slight gain in thrust due to mass flow increase from the inducted ambient air which can increase the overall momentum of the exhaust gases.
The ultra hush exhaust system (uhes) is an ejector/eductor hush kit for airliners and general aviation business jets powered by what is referred to as low by-pass jet engines or turbojet engines which generate a very loud acoustic signature. This high acoustic signature results in noise pollution at airports and undesirable noise during approach, take-off or flying at low altitude over residential areas located near the approach path of airports. The ultra hush exhaust system is invented to retrofit the current exhaust system of these aircrafts or future supersonic aircrafts with the ultra hush exhaust system (uhes) to comply with strict airworthiness noise regulations which are not met by these types of aircrafts, thereby extending their service life.
The uhes ejector hush exhaust system adapts the ultra and/or square thrust reverser system, U.S. Pat. Nos. 5,615,834 and 7,043,897, with improvements to the clamshell doors to mitigate the effect of rudder blanking, and the actuation system. The reverser/eductor system decelerates the aircraft after landing and reduces the jet engine noise to acceptable noise levels during take-off and approach for landing to meet stricter airworthiness noise regulations. This in turn will extend the service life of this type of aircrafts instead of having to replace their engines with new quieter engines or disposing of the aircraft all together since it violates the noise regulations, which constitutes a major financial loss to the owner.
The uhes ejector design concept is based on SAE Aerospace Information Report AIR-1191 and method of calculation of the primary exhaust gas flow and secondary cold flow drawn from ambient air. Ejectors are used extensively in various aerospace applications for providing cooling air to various compartments in engines and aircraft systems. Ejectors, also referred to also as eductors, principle of operation relies on the high speed engine exhaust gases exiting the engine exit nozzle, with relatively lower static pressure than ambient surrounding air, entering a mixing duct entraining with it the ambient air which is at a higher static pressure which rushes towards the area of lower static pressure, thereby causing the ambient air to mix with the high speed exhaust gases, thereby reducing the exhaust gas's velocity and noise signature which is caused by the shear forces between static ambient air and the high speed exhaust gases, at or near sonic velocity at the exit plane from the Jet Engine.
Previous designs for ejector hush systems such as U.S. Pat. No. 3,820,630 shows an ejector nozzle noise suppressor for a jet engine exhaust is provided by an annular divergent body attached to an exhaust nozzle. The smallest diameter of the divergent body is larger than the diameter of the exhaust nozzle's exit to form an annular step which produces a shock wave in the exhaust as it passes the step. An annular shroud is disposed around the divergent body and causes outside air to pass through voids in the divergent body to mix with the jet exhaust gas. The divergent body includes a plurality of channels with separators between the channels.
U.S. Pat. No. 7,111,448 describes a jet nozzle mixer includes identically formed lobes mounted inside the original tailpipe installation to provide mixing. The mixer works to mix the engine internal bypass flow with the internal jet engine core flow to level the disparate flow velocities, to reduce the peak velocities from the jet engine core and increase the lower bypass velocities of the engine internal bypass flow, and thereby reduce noise. No external air is inducted into the mixing tailpipe. The internal lobe contours act as lifting flutes, causing mixing of the primary hot and cold flows to mix before exiting the nozzle. External lobe contours at the engine exit plane act as venturi chutes, accelerating the cooler ambient secondary air flow. The external lobes thus act collectively as an injector to force the cooler ambient secondary flow into the previously mixed primary flow as it exits the nozzle.
U.S. Pat. No. 3,710,890 describes an exhaust nozzle noise suppression system for turbojet engines based on a centerbody plug mounted to the engine. The exhaust flow from the engine is directed by the centerbody plug into the ejector airstream from ambient air. A duct shrouds the eductor system which is mounted to the centerbody plug using struts.
In combination, each of the components of the hush kit described herein reduces noise generated by the jet engine for compliance with Federal Aviation Administration noise reduction requirements.